Multimedia image frames having video/audio effects and diversities are basic requirements for image processing apparatus such as individual appliance or personal computers. Further, it is preferred to enhance video/audio effects and diversities of image frames with limited cost.
In a typical scaling-down/scaling-up procedure for an image frame, an on-screen resolution technology is employed to process the image frame by an image processing device for a real-time display on a screen. FIGS. 1(a) and 1(b) are functional block diagrams illustrating two image processing devices by means of on-screen technology in the prior art. The image processing device shown in FIG. 1(a) is used to perform scaling-down/scaling-up operations, whereas the image processing device shown in FIG. 1(b) further conducts an image overlay effect in addition to the scaling-down/scaling-up operations. The scaled image frame is combined with another image frame such as a static 2-D image frame and outputted in an on-screen mode as overlay images.
Referring to FIG. 1(a), the image processing device principally comprises a control unit 11, a memory 12 assigned to the image processing device by the operating system (OS) and a frame buffering and outputting processor 13. A video image signal V generated from a video apparatus such as a video recorder, a TV set, a VCD-ROM or a DVD-ROM, and having a data format selected from YUV422, RGB15, RGB16, RGB32, YcbCr420, and the like, is first stored into an image storage zone 121 of the memory 12 as an image frame S in response to an image storing signal A asserted by the control unit 11. Further, in response to a control signal C1 asserted by the control unit 11, a scaling-down/scaling-up procedure is performed on the image frame S and the scaled image frame is outputted in an on-screen mode by the frame buffering and outputting processor 13.
The image processing device in FIG. 1(b) comprises a control unit 21, a memory 22 assigned to the image processing device by the operating system (OS), a frame buffering and outputting processor 23, and further a two-dimensional (hereinafter, 2-D) graphic processor 24 and an image overlay processor 25. The video image signal V from a video device is first stored into the image storage zone 221 of the memory 22 as an image frame S1 in response to an image storing signal A asserted by the control unit 21. A 2-D image signal G is stored into a 2-D image storage zone 222 of the memory 22 as a static 2-D image frame S2. On the other hand, in response to the control signal C1 from the control unit 21, a scaling-down/scaling-up procedure is performed on the image frame S1 and the scaled image frame is outputted in an on-screen mode by the frame buffering and outputting processor 23. On the other hand, in response to another control signal C2 from the control unit 21, the 2-D image frame S2 is processed by the 2-D graphic processor 24. The processed video image frame and 2-D image frame are transferred into the image overlay processor 25 and outputted by means of the on-screen technology.
In order to exempt from image delay, the number of image frames displayed on the screen per second, for example by the device of FIG. 1(a), should be more than 30 in average, and the video images are temporarily stored in the image storage zone 221 of the memory 22 and then immediately performed thereon image scaling operations in the queues of the frame buffering and outputting processor 23. The scaled images are then outputted on a real-time basis. For purpose of easily performing the scaling-down operation in the vertical dimension, the required size of each queue of the frame buffering and outputting processor 23 varies with the compression ratios and the row numbers (in the horizontal dimension) of the images. In brief, the capacity of the queues has to be large enough for storing several complete rows of image at the same time so that the images scaled in the vertical dimension can be performed on the on-screen basis.
Such image processing device based on the on-screen technology, therefore, is cost-inefficient and design-inflexible because a large queue size is required. In addition, the control unit 11 is largely occupied in processing the image frames S and S1 due to the real-time display. Therefore, additional tasks for enhancing image quality, for example low pass filtering or high pass filtering, are not expected to be done by the control unit 11 in general cases. The high quality of image cannot be acquired.